Cutter head for dry-shavers

ABSTRACT

Cutter head for dry shavers having a cutter head frame and a stationary upper cutter and reciprocating driven lower cutter resiliently pressed against the upper cutter. The upper cutter forms a resilient frame and has cutter teeth and the upper cutter is clamped to the cutter head frame under initial stress and with slight curvature concave towards the lower cutter.

United States Patent 1191 Ktinig 51 Nov. 27, 1973 [54] CUTTER HEAD FOR DRY-SHAVERS 3,456,341 7/1969 Loner 30/34.] [75] Inventor: Reinhard K't'mig, Krumpendorf,

Austria Primary ExaminerOthell M. Simpson [73] Asslgneez U. S. PhllIpS Corporation, New Assistant Examiner Gary L. Smith Ymk, AttorneyFrank R. Trifa'ri [22] Filed: Aug. 25, 1971 21 App]. No.: 174,995

[63] Continuation of Ser. No. 841,882, July I5, 1969,

abandoned.

- Cutter head for dry shavers having a cutter head 52 US. Cl. 30/34.1, 30/346.51 frame and a Stationary "PP cutter and reciprocating 51 Int. Cl B26!) 19/20, B26b 19 04 driven lower Cutter resiliently P against the [58] Field of Search 30/34.1, 241, 43.92, upper cutter- The upper Cutter forms a resilient frame 30/34651 and has cutter teeth and the upper cutter is clamped to the cutter head frame under initial stress and with [56] References Cited slight curvatureconcave towards the lower cutter.

UNITED STATES PATENTS 12'Claims, 10 Drawing Figures Patented Nov. 27, 1973 3,774,300

I5 Sheets-Sheet l I r INVENTOR. RC LWAJFd filing} gh (2 h? T 65 29V flliys.

"Patented Nov. 27, 1973 3,774,300

3 Sheets-Sheet 2 UUUL IN VEN TOR.

5 6i wz'iczrcz K5 7 [9 Patented Nov. 27, 1973 3,774,300

3 Sheets-Sheet 3 gQl/l Q I Fig. I0

I INVENTOR. Eta L77 Asa/11 ff'c rmg 1 CUTTER HEAD FOR DRY-SHAVERS This is a continuation of application Ser. No. 841,882 filed July 15, 1969, now abandoned.

The invention relates to a cutter head for dryshavers, having at least one lateral trimmer, and a stationary upper cutter, against which a reciprocating driven lower cutter is resiliently pressed, is secured on a support frame of the cutter head. In one known cutter head of this kind the upper cutter of the lateral trimmer is formed as a bar carrying cutter teeth and secured with screws on the cutter head frame. It has appeared that such a design causes difficulties, especially in mass production, unless the upper cutter is formed from a very solid steel plate, which however is unfavourable for economic reasons. With such an upper cutter produced however from relatively thin material it can very easily become warped in the region of the cutter teeth or twisted, in which case the cutting effect is greatly reduced due to the fact that the cutting faces of the upper and lower cutters, which are ground with plane faces, no longer properly engage each other.

The invention avoids such difficulties in a simple way due to the fact that the upper cutter is formed as an inhe'rently resilient frame with cutter teeth provided on at least one frame part extending parallel to the direction of movement of the lower cutter, which frame is clamped on the cutter head frame under. initial stress and with slight curving which is concave towards the lower cutter. An upper cutter which in this way is under initial stress in the assembled condition achieves the object that its cutting face, equalizing out any distortion, orients itself with a plane surface in a position to co-operate precisely with the cutting face of the lower cutter. Moreover this renders possible simple assembly and simple replacement of the upper cutter.

It has further proved expedient to offset that frame part of the upper cutter, which carries the cutter teeth toward the lower cutter achieves the object that the cutting face of the upper cutter is still better oriented with plane surface, with simultaneous stiffening of the upper cutter frame.

On the cutter head frame, in the region if its four corners there is preferably provided a projection extending perpendicular to the plane of the cutter head frame, these projections each having a lateral recess oriented in the direction of movement of the lower cutter for the reception of the upper cutter frame while the upper cutter frame, when pushed into the recesses, is supported on the two side parts of the cutter head frame extending perpendicular to the direction of movement of the lower cutter, with slight curvature and initial stress, and bears on the stop faces of the recesses lying opposite to the cutter head frame. Due to these measures a satisfactory seating of the upper cutter frame on the cutter head frame is ensured, the fitting of the upper cutter frame being especially simple and without the need for additional securing elements or tools.

Such a design has proved especially advantageous if all the recesses are open towards the outside of the cutter frame head, the distance between the end faces, ex tending perpendicular to the direction of movement of the lower cutter, of each pair of recesses being aligned in the direction of movement of the lower cutter being of movement of the lower cutter are provided with further depression in stair form. This achieves the object that the upper cutter is seated on the cutter head frame especially securely and in a precisely defined position in relation to the direction of movement of the lower cutter.

In this connection it has further proved favourable if the inner edges of the frame parts of the upper cutter which extend parallel to the direction of movement of the lower cutter lie immediately beside the projections. This in fact also precisely defines the position of the upper cutter frame transverse to the direction of movement of the lower cutter.

It is further advisable to stagger the two projections staggered towards one another in the direction of movement of the lower cutter, with the projections of at least one of the two pairs of projections lying one behind the other in the direction of movement of the lower cutter. This measure ensures that in the fitting of the upper cutter frame the cutter teeth of one specific frame part always come to lie on one specific side of the cutter head frame.

In the designs as stated above the supporting of the upper cutter on the cutter head frame can be effected by pins inserted into the upper cutter and cooperating with the cutter head frame. An especially simple design 'is obtained if a nose or projection is arranged on each of the two sides of the cutter head frame extending perpendicular to the direction of movement of the lower cutter, for supporting the upper cutter frame.

To facilitate the fitting of the upper cutter frame it has proved favourable in the above-stated case if the free ends of the noses facing in the direction of movement of the lower cutter are bevelled.

The upper cutter frame can be connected with the cutter head frame in a very simple way due to the fact that the frame parts of the upper cutter extending parallel to the direction of movement of the lower cutter are supported on corresponding sides of the cutter head frame and that for the clamping of the upper cutter frame, with initial stressing andcurving thereof, support elements are detachably secured on the cutter head frame and engaging on these frame parts of the upper cutter which extend perpendicular to the direction of movement of the lower cutter.

As support elements in this case for example small plates screwable to the cutter head frame can be provided. The support elements are advantageously formed by the side parts of a U-shaped bracket which are provided with apertures with which they are resiliently snapped on to projections on the cutter head frame, so that again no tool is necessary for the fitting of the upper cutter frame.

The U-shaped bracket is expediently formed simultaneously as a support for springs which press the lower cutter of the lateral trimmer against the upper cutter frame.

Moreover in this connection it has proved advantageous if projections fitting into corresponding apertures in the upper cutter frame are provided on the cut- 'ter head frame for the securing of position of the upper equal to the clear internal width of the upper cutter frame in this direction, while at least one pair of recesses lying side by side perpendicular to the direction cutter frame.

The invention will be explained in greater detail hereinafter by reference to the drawing, in which some ex- FIG. 1 is a perspective exploded view of a first embodiment with a shaver part pivoted away from the cutter head frame and with lifted lateral trimmer upper cutter.

FIG. 2 illustrates the completely fitted cutter head according to FIG. 1, partially in section and partially in lateral elevation.

FIGS. 3 and 4 are sectional views illustrating the manner of assembling the upper cutter frame with its associated parts in the embodiment according to FIGS. 1 and 2.

FIGS. 5 to 7 show a second embodiment, only the parts of the cutter head which are essential to the invention being illustrated. In FIGS. 5 and 6 the upper cutter is represented in an intermediate position in assembly, namely in FIG. 5 in plan view and in FIG. 6 in a longitudinal section along the line VI-VI in FIG. 5, while FIG. 7 shows in lateral elevation the upper cutter frame already mounted on the cutter head frame.

In FIG. 8 a further embodiment is illustrated in which the upper cutter frame is clamped in with detachable support elements on the cutter head frame.

FIG. 9 shows partly in section and partly in elevation and FIG. 10 shows in longitudinal section an embodiment of the cutter frame in which the side parts of a U- shaped bracket are provided as support elements for clamping the upper cutter frame on the cutter head frame.

The cutter head according to FIGS. 1 and 2 comprises, a cutter head frame 1, on which are mounted a shaver part 2 with perforated cutter foil and two lateral trimmers 3 and 4. The shaving part 2 including the perforated cutter foil is hingeable away from the cutter head frame 1, as represented in FIG. 1. The lower cutter 5 of the shaver part, co-operating with the perforated cutter foil, is shown only in FIG. 2, but is omitted from FIG. 1, for the sake of clarity. The construction of the shaver part per se is immaterial to the present invention.

One common stationary upper cutter 6 is associated with both lateral trimmers 3 and 4. Moreover the two lateral trimmers 3 and 4 have one common lower cutter 7, which is placed upon the cutter head frame 1 for reciprocating movement in the direction of the double arrow 8. Each of the longitudinal edges extending parallel to the direction of movement of the lower cutter and protruding beyond the cutter head frame 1, the lower cutter carries a row of cutter teeth 9 and 10 respectively. The means for the reciprocating drive of the lower cutter 7 is not illustrated for the sake of simplicity and the means for the resilient pressing of the lower cutter against the upper cutter 6 is shown as spring 6a in FIG. 1 and spring 47 in FIG. 10, which is further described in the second to last paragraph of this specifica tion;

The upper cutter 6 common to the two lateral trimmers is formed according to the invention as an inherently resilient frame, where each frame part 11 and 12 extending parallel to the direction of movement of the lower cutter carries a row 13 and 14 respectively of cutter teeth which cooperate with the corresponding rows 9 and 10 respectively of cutter teeth of the reciprocable lower cutter 7. For operatively mounting the upper cutter frame 6 on the cutter head frame 1, the frame is provided adjacent its four comers respectively with projections 15a to 15d extending perpendicular to the plane of the cutter head frame. Each of these projections has a lateral recess 16a to 16d respectively oriented in the direction of movement of the lower cutter, into which the upper cutter frame 6 can be pushed. These recesses 16a to 16d are all directed towards'the outside of the cutter head frame, the distance between the end faces l7a-17d, extending perpendicular to the direction of movement of the lower cutter. Pairs of recesses 16a and 16d and 16b and respectively, are relatively aligned in the direction of movement of the lower cutter, being spaced apart a distance equal to the internal width L of the cut out portion or aperture of the upper cutter frame in this direction. Two recesses 16c and 16d relatively aligned in a direction perpendicular to the direction of movement of the lower cutter each have a further depression 18c and 18d respectively in stepped relation. Such further depressions could if desired also be provided in the case of all four recesses.

On each of the sides 19, 20 of the cutter head frame which extend perpendicular to the direction of movement of the lower cutter there is provided, for the supporting of the frame parts 21 and 22 of the upper cutter which likewise extend perpendicular to the direction of movement of the lower cutter a nose 23 and 24 respectively which possesses on its free end wedge-shaped bevels extending in the direction of movement of the lower cutter. These noses 23, 24 reach to the level of the recesses 16a, 16b and 16c, 16d, so that the upper cutter frame 6 can be inserted into the recesses only with slight curving concave towards the lower cutter.

The manner of fitting of the upper cutter frame 6 consists in that firstly the upper cutter frame is inserted with slight curving with the frame part 22 into the recesses 16c and 16d and against the end faces 17, while supporting part 22 on the nose 24, the frame part 21 of the upper cutter still being situated above the projections 15a and 15b, as illustrated in FIG. 3. The wedgeshaped formation of the free end of the nose 24 here favours this insertion operation, since the wedge faces act as a ramp surface for the frame part 22 and permit it to slide upwards until it bears on the upper edge of the nose. Thereupon the upper cutter frame is curved further and the frame part 22 is pushed into the further depressions 18c and 18d, of the recesses 16c and 16d respectively, as shown in FIG. 4. In this position the frame part 21 is swung downwardly into alignment with before the recesses 16a and 16b, whereupon the upper cutter frame is then pushed back, namely with repeated curving, urging the frame part 21 into the recesses 16a and 16b and against the nose 23, sliding up on its wedge-shaped end. In these manipulations the frame part 21 of the upper cutter will have again entered the recesses 16c and 16d, bearing on the nose 24. Now both frame parts 21 and 22 of the upper cutter are disposed for abutment with the end faces 17 of the recesses 16a-d, so that, regarded in the direction of movement of the lower cutter, a secure anchoring of the upper cutter frame on the cutter head frame is achieved.

In this way the upper cutter frame, as may be seen from FIG. 2, is secured on the cutter head frame under initial stress and with slight concave curving towards the lower cutter, supporting itself with the frame parts 21 and 22 each on a nose 23 and 24 respectively and abutting against the stop faces of the recesses 16a-d lying opposite to the cutter head frame. The initial stress under which the upper cutter frame is thus fitted on the cutter head frame in this case guarantees an exact alignment of the cutting faces of the cutter teeth rows, so that satisfactory co-operation with the associated teeth of the lower cutter is guaranteed. In this arrangement it will be apparent that the cooperating parts 1541-1511, 23, 24 and 30, function as a clamping means.

If the upper cutter frame is to be removed, the procedure is the converse of that in fitting, the frame part 22 having then first to be introduced into the depressions 18c, 18d.

As indicated diagrammatically in FIG. 1, the inner edges 25 and 26 of the frame parts 11 and 12 of the upper cutter which extend parallel to the direction of movement of the lower cutter extend directly beside the projections 16. In this way asecuring of position of the upper cutter frame on the cutter head frame is also achieved perpendicular to the direction of movement of the lower cutter.

Moreover in the case of the one pair of projections b and 150 lying one behind the other in the direction of movement of the lower cutter the two projections are arranged mutually staggered in relation to the direction of movement of the lower cutter. For this purpose the projection 15b, as may be seen from FIG. 1, is arranged somewhat further towards the inner side of the cutter head frame than is the projection 15c. The inner edge 26 of the frame part 12 is protrudes inwardly in the region 27 where it co-operates with the projection 15b. This achieves the object that in the fitting of the upper cutter frame one specific row of cutter teeth always comes to lie on one predetermined side of the cutter head frame, which is important for example when the two lateral trimmers 3 and 4 are provided with cutter teeth of different formations.

As may be seen from FIGS. 1 and 2, the frameparts 11 and 12 of the upper cutter carrying the cutter teeth are cranked at 28 in the cross-section extending perpendicular to the direction of movemnt of the lower cutter. Thus an especially exact alignment of the cutter teeth, regarded in the direction of movement of the lower cutter, is achieved with simultaneous stiffening of the upper cutter frame.

Ordinarily the cutter teeth of the cutters will be ground to form exact cutting faces. In the present case this is most expediently effected for the upper cutter with a device on which the upper cutter frame is secured in the same way as on the cutter head frame.

In FIGS. 5 to 7 a cutter head is illustrated having only one lateral trimmer 2. The upper cutter 6 of this lateral trimmer is again formed as a frame which in itself is resilient, the frame part 11 of which carries the row 13' of cutter teeth. The opposite frame part 12 here serves only as support surface for the lower cutter 7', as may be seen from FIG. 7.

In this example of embodiment the recesses 16a to 16d are all oriented in the same direction in the projections 15a to 15d provided on the cutter head frame 1. Thus the upper cutter frame 6 can be simply placed upon the cutter head frame and pushed into the recesses 16a to 16d in the direction of the arrow 29', as represented in FIG. 6. The supporting of the frame parts 21' and 22' of the upper cutter on the sides 19 and 20' respectively of the cutter head frame is here effected by the insertion of a pin 30 into each of the frame parts 21 and 22'. These pins snap into recesses 31 and 32' respectively formed in the side parts 19' and 20' of the cutter head whereby a securing of position of the upper cutter frame on the cutter head frame is achieved, apart from the supporting. The length of the pins or projections 30 is so selected that again a slightly concave curving towards the lower cutter and an initial stressing of the upper cutter frame are achieved, as may be seen from FIG. 7.

The frame part 11' of the upper cutter frame, carrying the cutter teeth, is again provided with a crank 28' in the cross-section extending perpendicular to the direction of movement of the lower cutter. Obviously, for the further stiffening of the upper cutter frame its frame part 12 could also be cranked in such away.

In the example of embodiment according to FIG. 8 the upper cutter 6", made as an inherently resilient frame, is guided to the cutter head frame from the under side of the latter, the frame parts 11" and'l2" of the upper cutter, which extend parallel to the direction of movement of the lower cutter bearing upon the side parts 33 and 34 of thecutter head frame which likewise extend parallel to the direction of movement of the lower cutter. In this case two support elements or clamping means 35 are provided for the clamping-in of the upper cutter frame on the cutter head frame. These clamping means are made in plate form and each includes a projection 37 protruding from one side face 36. On each side part 38 of the cutter head frame extending perpendicular to the direction of movement of the lower cutter such a support element is arranged for displacement in guides 39 extending perpendicular to the upper cutter frame and is fixable with a screw connection 40 in its correct position in relation to the cutter head frame ensuring curving of the upper cutter.

In this case themanner of fitting of the upper cutter frame consists in that, as mentioned, the upper cutter frame is applied to the side parts 33 and 34 of the cutter head frame, whereupon the support elements are inserted into the guides 39" and pushed to the frame parts 21" and 22" respectively of the upper cutter which extend perpendicular to the direction of movement of the lower cutter, until their side faces 36 exert such a pressure upon these frame parts that the upper cutter frame curves slightly. In this action the projections 37 of the support elements pass through corresponding apertures in the frame parts 21 and 22 of the upper cutter and thus constitute a securing of position for the upper cutter frame on the cutter head frame. Then the support elements are secured on the cutter head frame by means of the screw connection 40.

In the case of the example of embodiment according to FIGS. 9 and 10 the upper cutter frame 6" again bears, as in the example of embodiment according to FIG. 8, on the side parts 33' and 34" of the cutter head frame extending parallel to the direction of movement of the lower cutter. Here the two side parts 41 of a U-shaped bracket 42 serve as support elements or clamping means for the clamping in of the upper cutter frame on the cutter head frame. For the detachable securing of the U-shaped bracket on the cutter head frame an aperture 43" is provided in each of the two somewhat resilient side parts 41, which apertures cooperate each with one of projections 44 provided on the two frame parts 38" of the cutter head, in the form of a snap-in connection. When the U-shaped bracket is secured on the cutter head frame, the free ends of its side parts 41 press upon the frame parts 21" and 22" of the upper cutter extending perpendicular to the direction of movement of the lower cutter, so that the upper cutter is curved and initially stressed.

To secure the position of the upper cutter frame on the cutter head frame, on the side parts 33" and 34" of the latter there are arranged projections 45 which engage in fitting manner in corresponding apertures 46 provided in the frame parts 11" and 12' of the upper cutter.

This U-shaped bracket 42" is a support for springs 47" which press the lower cutter 7' against the upper cutter frame 6", whereby an especially simple overall assembly of the cutter head is obtained.

Obviously a series of modifications of the examples of embodiment as described is possible without departure from the scope of the invention. This applies especially to the manner in which the upper cutter frame is curved and clamped-in on the cutter head frame. Such a fastening of the upper cutter can also be used for example in the case of an apparatus intended for the cutting only of longer hair.

Having thus described my invention, 1 claim:

1. In a dry shaver cutting head including a cutting head frame, at least one lateral trimmer comprising a stationary upper cutter formed as a resilient upper cutter frame having two spaced parallel sides and two transverse end parts bridging said sides, and a row of cutter teeth on at least one of said sides, a lower cutter reciprocally movable in the direction of said sides and having teeth corresponding to and adjacent said upper cutter teeth, means for resiliently urging said lower cutter and its teeth against the upper cutter and its teeth respectively, first measn for attaching the upper cutter frame to the cutting head frame at points along said sides, second means supporting said upper cutter frame relative to said cutting head frame at points along said transverse ends intermediate said sides, said second means engaging said cutter frame end parts in pressure contact urging same into a concave curvature, with said concave surface facing said lower cutter.

2. A cutting head according to claim 1, in which the frame part of the upper cutter carries the cutter teeth in a plane offset from and parallel to the remainder of said upper cutter frame.

3. A cutting head according to claim 1, in which the cutting head frame is quadrangular and consists of (i) two side parts extending parallel to the direction of reciprocation of the lower cutter, and of (ii) two transverse parts, and in which, in the region of each of the four corners of the cutting head frame, there is said first means formed as a projection extending perpendicular to the plane of the cutting head frame, these projections each having a lateral recess open outward in the direction of movement of the lower cutter for reception of the transverse parts of the upper cutter frame, said transverse parts of the cutting head frame each also having a similarly extending support projection which is said second means, and the upper cutter frame, when its transverse parts are inserted into these recesses and engaged by said support projections, being flexed and maintained in a concave state.

4. A cutting head according toclaim 3 wherein said support projections are formed by a nose on each of the two transverse parts of the cutting head frame for supporting the transverse parts of the upper cutter frame.

5. A cutting head according to claim 3, in which the side parts of the upper cutter frame which extend parallel to the direction of movement of the lower cutter are clamped along two spaced lines to adjacent sides of the cutting head frame, while the support projections for supporting the transverse parts of the upper cutter frame are detachably secured to the cutting head frame.

6. A cutting head according to claim 3 wherein said upper cutter frame has a clear aperture of a given length between its transverse parts, and wherein each of said recesses has an outward facing end face, and the distance between a pair of opposite end faces of the recesses lying one behind the other in the direction of movement of the lower cutter is equal to said given length, while at least one pair of recesses lying side by side perpendicular to the direction of movement of the lower cutter are provided with a further depression in stair form.

7. A cutting head according to claim 3, in which the inner edges of the side parts of the upper cutter frame which extend parallel to the direction of movement of the lower cutter lie immediately beside said projections.

8. A cutting head according to claim 7, in which, in at least the projections of one of the two pairs of projections aligned one with the other in the direction of movement of the lower cutter, are closer together than projections of the other pair.

9. A cutting head according to claim 4, in which the noses facing normal to the direction of movement of the lower cutter, are bevelled.

10. A cutting head according to claim 5, wherein said cutting head frames transverse parts have engaging projections, and said second means comprise U-shaped brackets having apertures therein for resiliently engaging said engaging projections.

1 l. A cutting head according to claim 1, further comprising springs which press said lower cutter against the upper cutter frame.

12. A cutting head according to claim 1, further comprising said positioning projections on the cutter head frame, and corresponding apertures in the upper cutter frame, for engaging and positioning the upper cutter frame relative to cutter head frame. 

1. In a dry shaver cutting head including a cutting head frame, at least one lateral trimmer comprising a stationary upper cutter formed as a resilient upper cutter frame having two spaced parallel sides and two transverse end parts bridging said sides, and a row of cutter teeth on at least one of said sides, a lower cutter reciprocally movable in the direction of said sides and having teeth corresponding to and adjacent said upper cutter teeth, means for resiliently urging said lower cutter and its teeth against the upper cutter and its teeth respectively, first measn for attaching the upper cutter frame to the cutting head frame at points along said sides, second means supporting said upper cutter frame relative to said cutting head frAme at points along said transverse ends intermediate said sides, said second means engaging said cutter frame end parts in pressure contact urging same into a concave curvature, with said concave surface facing said lower cutter.
 2. A cutting head according to claim 1, in which the frame part of the upper cutter carries the cutter teeth in a plane offset from and parallel to the remainder of said upper cutter frame.
 3. A cutting head according to claim 1, in which the cutting head frame is quadrangular and consists of (i) two side parts extending parallel to the direction of reciprocation of the lower cutter, and of (ii) two transverse parts, and in which, in the region of each of the four corners of the cutting head frame, there is said first means formed as a projection extending perpendicular to the plane of the cutting head frame, these projections each having a lateral recess open outward in the direction of movement of the lower cutter for reception of the transverse parts of the upper cutter frame, said transverse parts of the cutting head frame each also having a similarly extending support projection which is said second means, and the upper cutter frame, when its transverse parts are inserted into these recesses and engaged by said support projections, being flexed and maintained in a concave state.
 4. A cutting head according to claim 3 wherein said support projections are formed by a nose on each of the two transverse parts of the cutting head frame for supporting the transverse parts of the upper cutter frame.
 5. A cutting head according to claim 3, in which the side parts of the upper cutter frame which extend parallel to the direction of movement of the lower cutter are clamped along two spaced lines to adjacent sides of the cutting head frame, while the support projections for supporting the transverse parts of the upper cutter frame are detachably secured to the cutting head frame.
 6. A cutting head according to claim 3 wherein said upper cutter frame has a clear aperture of a given length between its transverse parts, and wherein each of said recesses has an outward facing end face, and the distance between a pair of opposite end faces of the recesses lying one behind the other in the direction of movement of the lower cutter is equal to said given length, while at least one pair of recesses lying side by side perpendicular to the direction of movement of the lower cutter are provided with a further depression in stair form.
 7. A cutting head according to claim 3, in which the inner edges of the side parts of the upper cutter frame which extend parallel to the direction of movement of the lower cutter lie immediately beside said projections.
 8. A cutting head according to claim 7, in which, in at least the projections of one of the two pairs of projections aligned one with the other in the direction of movement of the lower cutter, are closer together than projections of the other pair.
 9. A cutting head according to claim 4, in which the noses facing normal to the direction of movement of the lower cutter, are bevelled.
 10. A cutting head according to claim 5, wherein said cutting head frames transverse parts have engaging projections, and said second means comprise U-shaped brackets having apertures therein for resiliently engaging said engaging projections.
 11. A cutting head according to claim 1, further comprising springs which press said lower cutter against the upper cutter frame.
 12. A cutting head according to claim 1, further comprising said positioning projections on the cutter head frame, and corresponding apertures in the upper cutter frame, for engaging and positioning the upper cutter frame relative to cutter head frame. 